This invention relates to a billet continuous casting machine and casting method which continuously pour molten metal into a tubular mold to solidify the molten metal, thereby continuously producing a cast piece of a square or rectangular cross sectional shape.
FIG. 7 is an explanatory drawing showing an example of a conventional billet continuous casting machine.
As shown in the drawing, molten metal (molten steel) is poured through a molten metal nozzle 101 into a mold 100. At this time, cooling water is sprayed from a plurality of spray nozzles 102, arranged outside the mold 100, to cool the mold 100. While the molten metal inside the mold 100 is gradually moving downward, its peripheral area is solidified. A cast piece 103 is continuously formed and forced out of the mold 100.
The cooling water is supplied by a pump or the like (not shown) through a cooling water inlet 104 into a jacket 105. The water flowing in the jacket 105 cools the surroundings of the mold 100, or cools the mold 100 by being sprayed from the spray nozzles 102 as mentioned above, and is then discharged through a cooling water outlet 106.
The mold 100 is in a tubular form having a square cross section, and is provided with a linear taper (inclination) ranging from a molten metal inlet at the top of the mold to a cast piece outlet at the bottom of the mold. The taper value of the mold 100 is 1% of less, and a generally used taper value is 0.6 to 0.8%.
As described above, a conventional billet continuous casting machine has the tapered mold 100, and cooling means for cooling the mold, and operates while suitably combining a cooling rate with the taper and the cooling means.
In the conventional billet continuous casting machine, the taper of the mold 100 was relatively small, and low speed casting posed few problems. High speed casting (3 m/min or more), however, caused the following insoluble problems: At the corners of a lower part of the mold 100, air gaps (gaps between the mold and a solid shell which are generated because of the nonuniform growth of the solid shell in the mold; gaps are generated at the corners of the lower part of the mold) appear between the mold 100 and the cast piece 103. Furthermore, the site of delay in solidification occurs in the cast piece from its corners as far as 10 mm or so apart, thereby deteriorating the quality of the product. That is, the occurrence of the air gaps makes the cooling of the cast piece 103 nonuniform, thus inducing deformation, cracks or structure defects of the cast piece 103. The occurrence of the site of solidification delay, moreover, causes rhombic deformation or breakout.